This invention relates to a magnetic recording-playback apparatus, and particularly to a video signal time axis altering circuit used in a magnetic recording-playback apparatus suitable for recording a broad-band video signal after dividing it into signals in multiple channels on a magnetic recording medium and a method therefor.
The development is under way for the so-called "high quality television system" which reproduces pictures in quality, particularly in fineness, incomparably higher than the conventional NTSC television system. The new system involves more image information and thus necessitates wider frequency band by several times than the conventional system.
A key subject to bring the high quality television system into practice is the achievement of a magnetic recording-playback apparatus, i.e., VTR, capable of recording a broad-band video signal and reproducing high quality pictures properly. A test-model VTR used for the high quality television system is described in the technical report of The Institute of Television Engineers of Japan, entitled "VTR for high quality television", by Oketani, Tateno and Tsujikawa, Vo. 8, No. 33, published in Nov. 1984. The VTR, which is oriented mainly to television broadcasting studios, employs a head drum in large diameter so as to deal with broad-band frequencies and records a video signal in a divided form on four-channel tracks on the magnetic tape.
In order for the high quality television system to prevail as a household appliance, the VTR used for the system must be compact, inexpensive, and capable of long-time recording on a small cassette tape. To meet these requirements, the head drum must be small in size, the magnetic heads and signal channels must be small in number, and the associated circuits must be as simple as possible. However, a greater amount of image information to be recorded on the magnetic tape results in an increased recording density on the tape, which imposes technical difficulties in practicing the VTR oriented to the high quality television system.